Packaging Code Flashcards
set a variable
variableName=”some value”
no spaces
access a variable
echo $variableName
set a variable before a command
What’s the lifetime of the variable
SOMETHING=”a value” env
The lifetime is just that one line
What happens with this:
$ SOMETHING=”something else” echo $SOMETHING
why?
SOMETHING not found
because variables are evaluated before the setting occurs
Change the prompt
PS1=’whatever’
PS1 is the variable for prompt
turn a variable into a command
newVariable=”echo”
$newVariable ‘a string or whatever’
Mix 2 srings
MESSAGE1=”This is message 1.”
MESSAGE2=”This is message 2.”
MESSAGE=”$MESSAGE1 $MESSAGE2”
echo $MESSAGE
This is message 1. This is message 2.
What happens with this:
MESSAGE=’$MESSAGE1 $MESSAGE2’
echo $MESSAGE
$MESSAGE1 $MESSAGE2
To ensure that variables will be interpolated, you must use double quotation marks (“), not single quotes (‘). Try the following example in your command line to see the difference:
A command is just a file.
How does the computer know where to look for that file?
If it doesn’t have /, ., or ~, it’s not a file name. It will then look in the paths of the PATH variable.
$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
looks in sbin first, then bin etc.
Find what folder a command in is
which man
which ls
Add a custom path but maintain the old ones
export PATH=”/path/to/my/executables-directory:$PATH”
So we’re setting path to our new option, then looks for the old options
Users/groups have certain permissions to files
t or f
F
Files have access given to certain users/groups
There’s nothing about a person that inherently gives them permission to dine at a restaurant at a particular table and at a particular time. It’s because the restaurant has labeled, or set apart, that table for that time that the person is able to dine there. So it is with the file system. There’s nothing inherently special about any group or user (except the root user). A user’s privileges are defined by the files and directories themselves.
Do something as root
sudo command
Enter root mode
sudo su
what is the general node project directory structure
.git .gitignore in main path
any code files in lib directory
any test files in test directory
Then a directory called assets, with more directories for images, css, js
How to only assign 1 module to a variable (using require(‘’))
multiple independent files like lodash
const chunk = require(‘lodash/chunk’);
console.log(chunk([1, 2, 3, 4, 5, 6, 7, 8], 2));
// logs [[1, 2], [3, 4], [5, 6], [7, 8]]
otherwise
const chunk = require(‘lodash’).chunk;
This code doesn’t solve the processing issue; Node still needs to read the entire module. However, thanks to garbage collection, it doesn’t put much strain on memory resources; the imported but unneeded names are immediately eligible for garbage collection.
What does the –save do in
npm install lodash –save
e save option tells npm to save the package to the dependencies list in package.json
can also do -S
What does the –save-dev do in
npm install eslint –save-dev
Sometimes, your project only needs a package during development. Such packages include code linters, debuggers, and minifiers. These tools aren’t part of the final application but are useful or necessary during development. Ideally, you should only install such tools in the development environment, not in production. Fortunately, package.json lets you identify such development dependencies by adding a devDependencies property. The easiest way to do that is to use npm install with the –save-dev option
https://launchschool.com/lessons/3f433bfc/assignments/2f0f28c7
what does npx do?
Since ESLint is an executable package, we’ll run it from the terminal. However, if you try to run eslint filename.js, it will use the globally installed eslint executable. The reason you install a package locally, though, is that you want to use that specific version of the package inside your project. Your globally installed version may not be compatible with your project for some reason.
There are several ways to run a local npm executable package, but the simplest way is to precede the executable’s name by npx:
The npx command uses the local version of eslint to scan the todolist.js file. Note that you don’t have to have the intended executable installed globally; npx merely checks for a local installation first. If it can’t find the package (eslint) locally or globally, it downloads and uses a temporary version of the named package.
Delete a dependency
Delete a dependency and remove it from the package.json
Delete a dependecny and removes development dependencies.
npm uninstall lodash
npm uninstall lodash –save
npm uninstall eslint –save-dev
You can also use npm prune to remove dependencies. This command is useful when you manually remove some dependencies from package.json and want to remove the packages from node_modules. For example, suppose that we edit package.json and delete morgan from the dependencies list, then run npm prune. Since morgan is no longer a dependency, npm prune removes it from node_modules.
How to install a package globally
add -g
Why install packages locally?
As a general rule, you should install almost all of your packages locally in your project’s node_modules directory. We recommend this practice highly. It ensures that projects that need specific versions of packages have them locally available. If another project needs a different version of a package, you can install that version in its node_modules directory. Since each package is local to the project, each project is free to use the version it needs.
What is transpilation?
Transpilation is the process of converting source code written in one language into another language with a similar level of abstraction to the original code. In the JavaScript world, it often means taking code written in a superset of JavaScript and rewriting it as plain JavaScript. Most often, that means converting code that uses the latest language features to an older version of the language. For instance, we may want to transpile a program written with ES6 features like let, class, and arrow functions into a form that lets it run in browsers that don’t recognize these features.
Automate a task with an npm script
“scripts”: {
“test”: “echo "Error: no test specified" && exit 1”,
“foo”: “echo ‘How do you do?’”
},
